Modular joint prosthesis

ABSTRACT

A modular hip joint prosthesis is assembled from a head section having a connection for the ball of the joint and from a shaft section. The shaft section is joined by a insert connection to the head section, and provision is made for fixing the insert connection. The insert connection is situated in the region of Shenton&#39;s arc. The respective contours, in longitudinal section, of the head and shaft sections in the region of the connection merge smoothly, without any substantial change in direction, irrespective of the relative mutual alignments of the sections at any given time, with the exception of a gap in the immediate vicinity of the connection.

FIELD OF THE INVENTION

The invention relates to a modular joint prosthesis comprising a headpart including a connection for a ball of the joint; a shaft partconnectable to the head part by an insert connection; and means forlocking the insert connection.

Joint prostheses are produced in the most various shapes and sizes,particularly as hip joint prostheses, to create good adaptation to theanatomical conditions of a given patient.

By means of a multi-part embodiment with nonpositive connection of thecorresponding individual parts in the proximal region, the adaptationcan be accomplished optimally. At the same time, positioning of thejoint head is possible regardless of the shaft diameter.

From European Patent Disclosure EP-B1 0 243 298, a kit for a shaftprosthesis is known, which has a head part that can be provided with ajoint ball, an end part anchored in the bone, and an intermediate partthat can be positioned between the two. All the parts have conical boresor complementary pegs, and as a result the prosthesis can be assembledby making conical insert connections. The head part and intermediatepart each have an axial through bore.

When the individual parts are put together, the corresponding bores arealigned axially in the direction of the shaft. The individual parts ofthe prosthesis are put together using a tie rod that transmits a forcein the axial direction and that penetrates both the head part andsucceeding shaft parts and can be screwed into the threaded bore of theend part. As a result, the head part, or the intermediate part, and theend part are firmly tightened against one another, so that loosening ofthe individual parts of the prosthesis from the mechanical strain duringuse need not be feared.

The prosthesis described in EP 0 243 298, however, is not bent and is,therefore, not optimally adapted to the anatomy of the hip joint.Furthermore, in other previously known hip joint prostheses, a universalversion, that is, one that can be used for the majority of disease casesto be expected, is unattainable.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, it is the object of theinvention to create a modular hip joint prosthesis of the generic typereferred to at the outset, which by the embodiment of its individualparts offers the possibility of producing a universal usable prosthesis.

The above and other objects are accomplished according to the inventionby the provision of a modular hip joint prosthesis comprising: a headpart, including a connection for a ball of the joint; a shaftconnectable to the head part in a connection region having a curvedcontour region, in longitudinal section, corresponding to Shenton's arc,the head part including a distal region and the shaft part including aproximal region that together define an insert connection havingperipheral edges separated by a gap in the curved contour region; andmeans for locking the insert; wherein the head part and the shaft parthave respective contours in the connection region, in longitudinalsection, which merge with one another without substantially changingdirection, regardless of a particular relative alignment of the head andshaft parts, except for the gap in the connection region.

The invention encompasses the recognition that by embodying a hip jointprosthesis in two parts, favorable conditions are present for universaluse of it, if the resultant structural form, regardless of the type ofassembly, is adapted to the form of a modern standard prosthesis. Thishas been attained with the provisions of the invention, regardless ofthe alignment of the shaft end relative to the head part. Care is takenparticularly to assure that the insert connection for connecting theshaft parts is located in a region which, when it is adapted to theevacuated marrow space, does not require any recesses or widenedportions in order to be received. With the provisions of the invention,a shaft prosthesis can be created which enables it to be designed for anindividual patient while still having the usual dimensions (andparticularly with precise adaptation to the evacuated interior of thebone). This can be done with a minimum number of component units thathave to be kept on hand, and can thus be done economically.

At the same time, this is also a prerequisite for being able to producea hip joint prosthesis that can be implanted on the left side, havingall intermediate positions also be possible, using a right-sideimplantable prosthesis, merely by pivoting the prosthesis head part 180°about the longitudinal axis of the insert connection. Because the shaftregion under the connecting location widens conically, once again asecure introduction of force into the bone is assured, so that theconnecting region itself is relieved.

With the provisions of the invention, even extremely long prostheses canbe put together in various configurations; because of the possibility ofoptimal shape adjustment by rotation in the connecting region, theoptimal seating of each prosthesis assembly in anatomically correct formis assured. With the means of the invention, using a prosthesis kit, itis accordingly possible to provide an individual accurate fit of aprosthesis made for an individual patient.

In accordance with a preferred embodiment of the invention, the hipjoint prosthesis provided for cementless implantation can be puttogether from a head part and a shaft part. A conical peg is provided onthe proximal end of the shaft part, and a recess of correspondingdimensions is provided on the distal end of the head part, forming aninsert connection once the joint prosthesis has been put together. Thehead part is divided up into a base and a connection peg intended tocarry the ball of the joint. The cross-sectional profile of the base ofthe head part is embodied substantially elliptically, and the longhalf-axis of the cross-sectional ellipse decreases continuously in thedistal direction.

One profiled section each, comprising axially extending ribs withrounded outer edges, is provided on the dorsal and frontal side faces ofthe head part. This advantageously creates a large surface area, whichpromotes fixation of the prosthesis by the ingrowth of bone material.

Preferably, the base of the head part has a longitudinal sectionalprofile, in a dorsal/frontal view, that widens in the proximal directionand is bounded on its lateral side by two straight lines forming anobtuse angle and on its medial side by a concave arc region. Thedistally located straight line of the pair of straight lines and the arcsegment continue in a respective straight line, which bound the distallyconically tapering longitudinal sectional profile of a proximal portionof the flat located below the insertion cone.

The straight lines of the pair of straight lines of the head partprofile are of different lengths and each has an inclination in thedirection of the center axis of the head part, and the shorter straightline is located on the distal end of the head part.

In a favorable further feature of the invention, a ratio of the lengthsof the straight lines in a range from 6 to 10 is provided.

The proximal end of the shaft part is embodied as a straight truncatedcone tapering in the distal direction, which on its distal end changesover, without shoulders, into a substantially cylindrically embodiedshaft portion. The diameter of the proximal circular face of thetruncated cone is equivalent to the length of the long half-axis of thetotal elliptical cross-sectional area on the distal end of the headpart. However, it is greater than the length of the short half-axis ofthis cross-sectional area. The resultant slight protrusion of the shaftpart from the dividing point creates additional anchoring of the shaftpart when the hip joint prosthesis is implanted, and this favorablycounteracts loosening of the shaft in the event that a medicallynecessary replacement of the head part has to be performed.

For the height of the truncated cone, a value of one-fourth to one-fifththe effective shaft length is favorable.

In another further feature of the invention, the cylindrical portion ofthe shaft part has profiling in the form of axially extending ribs,whose peripheral edges are rounded. The ribs are distributed uniformlyon the circumference of the shaft. The cylindrically embodied portion ofthe shaft part has a frontally oriented uniform curvature, and thusadvantageously creates preconditions for adapting the prosthesis to theanatomy of the upper thigh bone.

In another advantageous embodiment of the invention, the shaft part hasa longitudinal bore extending in the direction of the shaft axis. Thislongitudinal bore terminates on its distal end in at least one lateralopening in the shaft wall. The lateral opening is embodied as an oblongslot. It serves on the one hand to equalize pressure on insertion of thehip joint prosthesis, and on the other hand favorably allows the outflowof medications, which can be introduced by placing a medicationdispenser on the distal end of the longitudinal bore of the shaft part.The mean diameter of the longitudinal bore therefore has a value whichenables the positioning of the medication dispenser in the vicinity ofthe wall openings in the distal region of the shaft part.

In another further feature of the invention, a through bore extendingcrosswise to the shaft axis is provided between the distal end of thelongitudinal bore of the shaft part and the distal shaft end, in orderto receive further fixation means. The diameter of the transverse boreis selected such that the possibility exists of inserting a Kuntscherintermedullary nail. The use of fixation means on the distal shaft endof the hip joint prosthesis increases the security against twisting andthe axial load-bearing capacity of the prosthesis.

Since the bending stress acting on the endoprosthesis is not constantover time, but instead is subject to fluctuations in amount anddirection depending on the natural stress conditions of theendoprosthesis, microscopic motions occur between the peg and the bore.These microscopic motions, in combination with the local peak tensionsoccurring at the edge of the mouth of the bore, can cause abrasion ofmaterial and thus premature wear, which is also called fretting.

The local peak tensions occurring at the edge of the mouth of the boreare due to the fact that given a largely rigid peg reception, if the pegand bore are offset because of a bending stress, the effectivetension-absorbing contact area is reduced. In an extreme case, the pegtouches the inner wall of the bore only indirectly at the edge of themouth and on the opposite end on the bottom of the bore.

In an advantageous further variant of the invention, with its ownpatentable significance, the elasticity of the shaft element istherefore increased shortly before the end of the mouth of the conicalbore, so that the inner wall of the bore, in the event of a bendingstress on the endoprosthesis and thus attendant with staggering of thelongitudinal axes of the peg and the bore, adapts to the position of theleg and with the jacket face of the peg forms a sufficiently largetension-absorbing contact area. The immediate end of the cone maintainsthe same wall thickness, however, in order to preserve adequate strengthhere. Therefore the introduction of force in the end region of the coneis distributed over a greater length, thus avoiding excessive strain inthe immediate region of the mouth.

To that end, the head part or shaft part with the conical bore, on itsoutside at the level of the bore, has a notch that extends at leastpartway around relative to the longitudinal axis of the bore. As aresult, the wall thickness of the peg receptacle is reduced, whichincreases its resilience. Upon a bending stress on the joint prosthesisand a consequent staggering of the peg and bore relative to one another,the inner contour of the bore therefore adapts to the position of thepeg, and the tension-absorbing contact area between the peg and the boreis reduced only slightly, which results in a lesser mechanical stress atthe edge of the mouth of the bore and thus reduces mechanical wear.

By the weakening of the material as a result of the notch, theintroduction of force takes place not initially as a maximum peak at theend of the mouth of the conical bore but rather in evened-out fashionover the entire contact area of the peg and bore. Because of thisevening out of the force introduction, the maximum value for themechanical tension is reduced, and an overload on the material is thusprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous further features of the invention are described in furtherdetail below along with the description of the preferred embodiment ofthe invention, in conjunction with the drawings. Shown are:

FIG. 1, a dorsal and frontal view in fragmentary longitudinal section ofa preferred embodiment of the invention;

FIG. 2, a side view of the embodiment of the invention shown in FIG. 1;

FIG. 3, a sectional view taken along the line A . . . A of FIG. 1;

FIG. 4, a further section taken along the line B . . . B of FIG. 1;

FIG. 5, a modification of the joint prosthesis shown in FIG. 1, in afragmentary sectional view;

FIG. 6, again in a fragmentary sectional view, the head part of thejoint prosthesis shown in FIG. 5; and

FIG. 7, a detail of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIGS. 1 and 2, the preferred embodiment of the invention is shown infragmentary longitudinal section, in a dorsal/front view and in alateral view, respectively. The hip joint prosthesis 1 comprises a shaftpart 2 and a head part 3, which are taken from a kit for modular hipjoint prostheses in which essentially identically embodied head partsand shaft parts of various sizes are provided. The particular individualelements 2, 3 selected can preferably be connected to one another byputting together their respective proximal or distal ends that havecorresponding conical pegs 29 or recesses 30. The requisite stability ofthe insert connection is assured by means (not shown)--preferablyembodied as a tie rod. The respective shaft part 2 is embodied as ahollow shaft, and the axially extending longitudinal bore 5 on itsproximal end portion is embodied as a threaded bore 5.1. The tie rod(not shown) is passed through a cylindrical channel 4 in the head part3, located on the same axis as the longitudinal bore 5 in the shaft part2, and screwed into the threaded bore 5.1 of the shaft part 2.

The base 15 of the head part 3 has a longitudinal sectional profile, ina dorsal/frontal view, that widens in the proximal direction and isbounded on its lateral side by two straight lines 13, 14 forming anobtuse angle and on its medial side by a concave arc region 12. Thedistally located straight line 13 of the pair of straight lines 13, 14and the arc segment 12 continue in a respective straight line 10, 11,which bound the distally conically tapering longitudinal sectionalprofile of a proximal portion 2.1 of the flat 2 located below theinsertion cone.

It can be seen that in the connecting region of the side view, shown inFIG. 2 the side lines merge without essentially changing pitch from theproximal portion 2.1 of the shaft part 2 to the head part 32. In fact,this is true, independent of the relative angular orientation of theshaft part 2 and the head part 3; thus, the outer surface of theprosthesis appears without remarkable discontinuities, regardless ofsuch angular orientation. In this way, first--with a curved shaftpart--a left-side or right-side prosthesis is selectively created,without reducing the continuity of the shape contour. However, sinceintermediate positions can be attained without difficulty while at thesame time preserving the optimal contour course, the seat of theprosthesis can be adapted very precisely to the individual conditions.This is also true for long shafts, which are available in variouslengths as a substitute for a bone nail. Thus with a minimum number ofbasic elements, it is possible to meet a maximum number of needs inentirely different cases.

The straight lines 13, 14 have different lengths and each has aninclination in the direction of the center axis of the head part 3, withthe shorter straight line 13 located on the distal end of the head part3. A value in the range from 6 to 10 is contemplated for the ratio oflengths of the straight lines 13, 14.

As shown in FIG. 2 the proximal end of the shaft part 2, is embodied asa straight truncated cone 2.1, tapering in the distal direction, whichon its distal end changes over without shoulders into a shaft portionembodied essentially cylindrically, and having a continuous curvature inthe frontal direction. This kind of shaping on the proximal shaft endadvantageously assures a firm seat of the shaft part in the marrow spaceof the upper thigh bone. For the height of the truncated cone 2.1,one-fourth to one-fifth of the effective length of the shaft part 2(that is, of the shaft portion to be introduced into the marrow space)is favorable. The diameter of the proximal circular area of thetruncated cone 2.1 is equivalent to the length of the long half-axis ofthe total elliptical cross-sectional area on the distal end of the headpart 3. However, it is greater than the length of the short half-axis ofthe aforementioned cross-sectional area. The resultant slight protrusion17 of the shaft part 2 at the dividing point 18 creates additionalanchoring of the shaft part 2 when the hip joint prosthesis 1 isimplanted, which favorably counteracts loosening of the shaft in theevent that a medically necessary replacement of the head part has to beperformed.

The opening 6 in the wall of the shaft part 2 forms the distal end ofthe longitudinal bore (see reference numeral 5 of FIG. 1) of the shaftof the hip joint prosthesis 1. It is embodied as a longitudinal slot andserves on the one hand to allow the outflow of medication form amedication dispenser (not shown) positioned at the end of thelongitudinal bore, and on the other hand to equalize pressure when thehip joint prosthesis 1 is introduced by its shaft part 2 into theprepared marrow space of an upper thigh bone.

The through bore 7 on the distal end of the prosthesis shaft extendscrosswise to the axis of the shaft part 2. This bore is intended toreceive a fixation means, such as a locking nail, and is adapted in itsdiameter to the possible dimensions of the nail. The use of additionalfixation means advantageously increases the security against twistingand the axial load-bearing capacity of an implanted prosthesis.

It will be appreciated that according to the invention, even extremeshaft lengths, for applications in which until now nails had to beemployed, can be provided as shaft prostheses.

In FIGS. 3 and 4, a cross-sectional profile of the head part 3 (sectionalong the line A . . . A of FIG. 1) and a cross-sectional profile of theshaft part 2 (section along the line B . . . B of FIG. 1), respectively,are shown. The ribs 8, 9 extending axially, respectively on the broadsides of the head part 3 and on the periphery of the shaft part 2, arebounded peripherally by circular arcs. The through bore in theelliptical cross-sectional profile of the head part 3 is shown at 4, andthe central longitudinal bore of the shaft part 2 is shown at 5.

The joint prosthesis 19 shown in cross section in FIG. 5 is a furtherimprovement of the joint prosthesis shown in FIG. 1; the jointprosthesis 19 shown here has increased mechanical strength and reducedwear.

The joint prosthesis 19 shown--like the joint prosthesis shown alreadyin FIG. 1--especially comprises a head part 20 and a shaft part 21connected to it by a cone connection. The mechanical connection of thehead part 20 and shaft part 21 is accordingly accomplishednonpositively, in that a conical peg 22 formed onto the shaft part 21 isinserted into a conical bore 31 disposed in the head part 20 and withthis bore forms a press fit. To brace the head part 20 and shaft part 21against one another, a tie rod is used, which passes through a channel23 in the head part 20 and screwed into a threaded bore 24 in the shaftpart 21.

In such joint prostheses, the problem exists that upon a bending stresson the joint prosthesis, relatively high mechanical tensions occur atthe edge of the mouth of the conical bore. The peak mechanical tensionsat the edge of the mouth of the conical bore are due to the fact thatupon a bending stress on the joint prosthesis 19, the peg 22 and borebecome offset from one another, which causes a decrease in the effectivetension-absorbing contact area between the peg 22 and bore.

In an extreme case, the peg 22 now touches the inner wall of the boreonly unilaterally, respectively directly at the edge of the mouth and onthe opposed side directly on the bottom of the bore. The reduction inthe effective tension-absorbing contact area therefore createsrelatively high mechanical tensions, particularly at the edge of themouth of the bore.

Since the bending stress acting on the joint prosthesis 19 is notconstant over time but instead is subject to fluctuations in amount anddirection depending on the natural stress states of the joint prosthesis19, microscopic motions occur between the peg 22 and the bore. Thesemicroscopic motions, in combination with the local peak tensionsoccurring at the edge of the mouth of the bore, can cause abrasion ofmaterial and thus premature wear, which is also called fretting.

To reduce these wear phenomena, the head part 20--in contrast to thejoint prosthesis shown in FIG. 1--therefore has a notch 25, encompassingit on the outer wall near the lower end with regard to the longitudinalaxis of the bore. As a result of this notch 25, the wall thickness ofthe head part 20 is reduced, thus increasing the resilience of the pegreceptacle in the face of an offset of the peg 22. If the peg 22 isoffset relative to the bore as the result of a bending stress on thejoint prosthesis 19, then the peg receptacle--that is, the internalcontour of the bore--yields to the peg 22 and adapts to the alteredposition of the peg 22.

By this elastic adaptation of the peg receptacle, the effectivetension-absorbing contact area between the bore and peg is reduced onlyinsubstantially, even in the event of a bending stress on the jointprosthesis 19, which leads to a reduction in the mechanical stressoccurring at the edge of the mouth of the bore and reduces the wear onthe joint prosthesis 19.

The cross-sectional view shown in FIG. 6 of the head part 20 of thejoint prosthesis shown in FIG. 5 clearly shows the shape and dispositionof the notch 25 in the head part 20. The notch 25 initially has a depththat increases along the longitudinal axis of the head part 20 towardits end.

On the one hand, it is thereby attained that the peg receptacle--thatis, the internal contour of the bore 26--adapts well to the alteredposition of the peg in the event of relatively slight bending stresseson the joint prosthesis and correspondingly slight offsets of the pegand bore 26, and this, despite the offsetting of the peg and bore 26,leads to a relatively large effective tension-absorbing contact areabetween the peg and bore 26, and hence to a reduction in the mechanicalstress.

On the other hand, because of the resilience of the peg receptacle,which decreases toward the top along the longitudinal axis of the headpart 20, it is assured that the peg receptacle--that is, the internalcontour of the bore 26--yields only insubstantially, in response tomajor bending stresses of the joint prosthesis, which yielding isindispensable for a secure, largely play-free guidance of the peg. Thepeg receptacle is accordingly relatively soft in the face of relativelyslight bending stresses, which leads to a reduction in the mechanicaltensions at the edge of the mouth of the bore 26, but becomes harder asthe bending stress increases, which serves the purpose of secureguidance of the peg.

The notch 25 on the one hand leads to a reduction in the mechanicaltension at the edge of the mouth of the bore 26. On the other hand,however, the notch 25 represents a mechanical weak point in the headpart 20, which involves the risk of crack formation and consequentmechanical failure of the joint prosthesis. To reduce this risk, thenotch 25 has a smooth shape, without protruding or indented corners oredges. Thus on its upper end, the notch 25 terminates smoothly in theouter wall of the head part 20, without forming any kink or even ashoulder. As a result, the notch tensions that occur in the notch 25,and hence the danger of crack formation, are reduced.

FIG. 6 also shows the course of the mechanical stress, occurring in thepeg receptacle, along the longitudinal axis of the bore 26. The dashedline, for comparison, shows the course of tension in the jointprosthesis shown in FIG. 1, while the solid line shows the course ofmechanical tension in the above-described joint prosthesis having thenotch 25.

In the joint prosthesis of FIG. 1, the course of the mechanical tensionalong the longitudinal axis of the bore (not labeled in FIG. 1)corresponding to bore 26 is very highly nonlinear. Thus, the tension inthe upper region of the bore 26 is relatively slight, while in thevicinity of the edge of the mouth it increases up to the valueδ_(max),old.

In the above-described joint prosthesis, the course of tension along thelongitudinal axis of the bore 26 is conversely substantially moreuniform, which advantageously results in a substantially lesser maximumtension δ_(max),new.

The form of the notch 25 can be seen in more detail from FIG. 7, whichshows the detail I of FIG. 6. This illustration clearly shows that thenotch 25 is asymmetrical and has a depth that increases toward the endof the peg. Accordingly the notch 25 has two flanks 27, 28 of differentpitch; the flank 27 toward the end of the peg extends relatively steeplyand has only a slight length, while the flank 28 remote from the end ofthe peg extends relatively shallowly but is elongated and terminates atthe peg wall.

The invention is not limited in its realization to the preferredexemplary embodiment described above. On the contrary, a number ofvariants are conceivable, which make use of the provisions described,even in fundamentally different types of embodiments.

What is claimed is:
 1. A modular hip joint prosthesis, comprising:a headpart, including a connection for a ball of the joint; a shaft partconnectable to the head part in a connection region having a curvedcontour region, in longitudinal section, corresponding to Shenton's arc,the head part including a distal region and the shaft part including aproximal region that together define an insert connection havingperipheral edges separated by a gap in the curved contour region; andmeans for locking the insert connection; wherein the head part and theshaft part have respective contours in the connection region, inlongitudinal section, which merge with one another without substantiallychanging direction, regardless of a particular relative alignment of thehead and shaft parts, except for the gap in the connection region; andwherein: the head part and/or the shaft part has a conical bore on itsunderside; the shaft part, on its top side, has a conical peg adapted tothe conical bore, for connection to the head part or a further shaftpart; and a notch in the head part and/or the shaft part, extending allthe way around on the outer wall in the vicinity of the end of the mouthof the conical bore, which notch reduces the mechanical stress occurringdue to a bending stress at the edge of the mouth of the conical bore. 2.The modular hip joint prosthesis of claim 1, wherein the shaft partincludes a region that widens frustoconically toward the head part in aproximal portion of the shaft part in the connection region.
 3. Themodular hip joint prosthesis of claim 2, wherein the inclination of thefrustoconically widening region of the shaft part is continued by theinclination of the curved contour region of the head part in theconnection region.
 4. The modular hip joint prosthesis of claim 1,wherein a proximal region of the head part has a longitudinal sectionalprofiled in a dorsal/frontal view that widens in the proximal directionand is bounded on its lateral side by two straight lines forming anobtuse angle and on its medial side by a concave arc segment, whereinthe distally located straight line of the two straight lines and the arcsegment continue in respective straight lines, which bound the distallyconically tapering longitudinal sectional profile of a proximal portionof the shaft part located below an insertion cone located on theproximal end of the shaft part and forming part of the insertionconnection.
 5. The modular hip joint prosthesis of claim 1, wherein abase portion of the head part has a substantially ellipticalcross-sectional profile.
 6. The modular hip joint prosthesis of claim 5,wherein the long half-axis of the cross-sectional ellipse decreasescontinuously in the distal direction.
 7. The modular hip jointprosthesis of claim 1, wherein the proximal end of the shaft partconstitutes an insertion cone, and wherein the proximal portion of theshaft part below the insertion cone is embodied as a truncated cone,which tapers distally down to the terminal diameter of the shaft part.8. The modular hip joint prosthesis of claim 7, wherein the length ofthe truncated cone is equivalent to one-fourth to one-fifth theeffective shaft length.
 9. The modular hip joint prosthesis of claim 7,wherein a portion of the shaft part adjoining the distal end of thetruncated cone has a uniform curvature in the frontal direction.
 10. Themodular hip joint prosthesis of claim 1, wherein the shaft part has alongitudinal bore extending in the direction of the shaft axis.
 11. Themodular hip joint prosthesis of claim 10, wherein the longitudinal boreends on its distal end in at least one lateral opening in the shaftwall.
 12. The modular hip joint prosthesis of claim 11, wherein thelateral opening has the form of an oblong slot.
 13. The modular hipjoint prosthesis of claim 10, wherein the distal end of the shaft partcontains a transverse bore, for receiving an additional fixation means.14. The modular hip joint prosthesis of claim 1, further including aprofile comprising axially extending ribs with rounded outer edges onthe broad sides of a base portion of the head part.
 15. The modular hipjoint prosthesis of claim 1, wherein the shaft part has a longitudinalprofiling comprising ribs with rounded edges.
 16. The modular hip jointprosthesis of claim 15, wherein the ribs are distributed uniformly overthe circumference of the shaft part.
 17. The modular hip jointprosthesis of claim 1, wherein the depth of the notch increases partwayalong the longitudinal axis of the bore toward the end of the head part.18. The modular hip joint prosthesis of claim 1, wherein the notch isshaped such that, upon occurrence of a bending stress, the mechanicaltension at the edge of the mouth of the conical bore along thelongitudinal axis of the bore is essentially uniform, at least in thevicinity of the mouth of the conical bore.
 19. The modular hip jointprosthesis of claim 4, wherein the proximally located straight line ofthe two straight lines is inclined, in the proximal direction, towardthe longitudinal axis of the prosthesis.